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<a name="Extensions-implemented-in-GNU-Fortran"></a>
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<p>
Next: <a href="Extensions-not-implemented-in-GNU-Fortran.html#Extensions-not-implemented-in-GNU-Fortran" accesskey="n" rel="next">Extensions not implemented in GNU Fortran</a>, Up: <a href="Extensions.html#Extensions" accesskey="u" rel="up">Extensions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Extensions-implemented-in-GNU-Fortran-1"></a>
<h3 class="section">5.1 Extensions implemented in GNU Fortran</h3>
<a name="index-extensions_002c-implemented"></a>

<p>GNU Fortran implements a number of extensions over standard Fortran.
This chapter contains information on their syntax and meaning.  There
are currently two categories of GNU Fortran extensions, those that
provide functionality beyond that provided by any standard, and those
that are supported by GNU Fortran purely for backward compatibility
with legacy compilers.  By default, <samp>-std=gnu</samp> allows the
compiler to accept both types of extensions, but to warn about the use
of the latter.  Specifying either <samp>-std=f95</samp>,
<samp>-std=f2003</samp>, <samp>-std=f2008</samp>, or <samp>-std=f2018</samp>
disables both types of extensions, and <samp>-std=legacy</samp> allows
both without warning.  The special compile flag <samp>-fdec</samp> enables
additional compatibility extensions along with those enabled by
<samp>-std=legacy</samp>.
</p>
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<tr><td align="left" valign="top">&bull; <a href="Old_002dstyle-kind-specifications.html#Old_002dstyle-kind-specifications" accesskey="1">Old-style kind specifications</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Old_002dstyle-variable-initialization.html#Old_002dstyle-variable-initialization" accesskey="2">Old-style variable initialization</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Extensions-to-namelist.html#Extensions-to-namelist" accesskey="3">Extensions to namelist</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="X-format-descriptor-without-count-field.html#X-format-descriptor-without-count-field" accesskey="4">X format descriptor without count field</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Commas-in-FORMAT-specifications.html#Commas-in-FORMAT-specifications" accesskey="5">Commas in FORMAT specifications</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Missing-period-in-FORMAT-specifications.html#Missing-period-in-FORMAT-specifications" accesskey="6">Missing period in FORMAT specifications</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Default-widths-for-F_002c-G-and-I-format-descriptors.html#Default-widths-for-F_002c-G-and-I-format-descriptors" accesskey="7">Default widths for F, G and I format descriptors</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="I_002fO-item-lists.html#I_002fO-item-lists" accesskey="8">I/O item lists</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Q-exponent_002dletter.html#Q-exponent_002dletter" accesskey="9"><code>Q</code> exponent-letter</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="BOZ-literal-constants.html#BOZ-literal-constants">BOZ literal constants</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Real-array-indices.html#Real-array-indices">Real array indices</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Unary-operators.html#Unary-operators">Unary operators</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Implicitly-convert-LOGICAL-and-INTEGER-values.html#Implicitly-convert-LOGICAL-and-INTEGER-values">Implicitly convert LOGICAL and INTEGER values</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Hollerith-constants-support.html#Hollerith-constants-support">Hollerith constants support</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Character-conversion.html#Character-conversion">Character conversion</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Cray-pointers.html#Cray-pointers">Cray pointers</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="CONVERT-specifier.html#CONVERT-specifier">CONVERT specifier</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OpenMP.html#OpenMP">OpenMP</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OpenACC.html#OpenACC">OpenACC</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Argument-list-functions.html#Argument-list-functions">Argument list functions</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Read_002fWrite-after-EOF-marker.html#Read_002fWrite-after-EOF-marker">Read/Write after EOF marker</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="STRUCTURE-and-RECORD.html#STRUCTURE-and-RECORD">STRUCTURE and RECORD</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="UNION-and-MAP.html#UNION-and-MAP">UNION and MAP</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Type-variants-for-integer-intrinsics.html#Type-variants-for-integer-intrinsics">Type variants for integer intrinsics</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="AUTOMATIC-and-STATIC-attributes.html#AUTOMATIC-and-STATIC-attributes">AUTOMATIC and STATIC attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Extended-math-intrinsics.html#Extended-math-intrinsics">Extended math intrinsics</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Form-feed-as-whitespace.html#Form-feed-as-whitespace">Form feed as whitespace</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="TYPE-as-an-alias-for-PRINT.html#TYPE-as-an-alias-for-PRINT">TYPE as an alias for PRINT</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="_0025LOC-as-an-rvalue.html#g_t_0025LOC-as-an-rvalue">%LOC as an rvalue</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="_002eXOR_002e-operator.html#g_t_002eXOR_002e-operator">.XOR. operator</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Bitwise-logical-operators.html#Bitwise-logical-operators">Bitwise logical operators</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Extended-I_002fO-specifiers.html#Extended-I_002fO-specifiers">Extended I/O specifiers</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Legacy-PARAMETER-statements.html#Legacy-PARAMETER-statements">Legacy PARAMETER statements</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Default-exponents.html#Default-exponents">Default exponents</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
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